I am surprised how some in this thread appear to have accepted the subscription basis for the site, as when N3V suggested a subscription-based service for the Trainz Next version of the simulator sometime back it was very much "shouted down" wholeheartedly by a great number of members on this forum.
A very interesting observation but I think that the difference may be due to TKI not being an absolute necessity for running Trainz while accessing the subscription services for TANE NEXT (or whatever) may not be optional - although I believe that the subscription suggestion may only have been "run up the flag pole" for a multi-player Surveyor option.
I have never used TKI as I don't use any assets from 3rd party sites and I probably would not be interested in using a multi-user Surveyor option - so a subscription on either would not bother me.